This invention relates to double-axis (2.times.1 unit) type key switches for use in key input devices, for example point of sale terminals or electronic cash registers.
Referring to FIG. 4, a typical conventional double-axis key switch 100 for a key input device includes a single piece housing 10 with two key stem guide sleeves 12, 12. Each of a pair of key stems 14, 14 fits slidably into a respective one of key stem guide sleeves 12, 12. Key stems 14, 14 slide downward when a key cap 16 is pressed. When key cap 16 is pressed, tips of coil springs 18, 18 that are set inside key stems 14, 14 are moved toward stationary contacts 24, 24 and 24, 24 on a printed wiring board 20 in housing 10. The tip of each coil spring 18 closes a switch by making electrical contact with a respective pair of stationary contacts 24, 24.
Double-axis key switch 100 is susceptible to the following problem when a downward force F is applied to a position away from a center point between key stems 14, 14. The key stems 14, 14 bind in their respective key stem guide sleeves 12, 12 due to friction between each key stem 14 and an inside surface at a mouth of a respective key stem guide sleeve 12. The force of this binding makes it difficult to operate double-axis key switch 100. Key stems 14, 14 may therefore fail to slide downwardly.
A known prior art, method for eliminating this problem is to use a connecting rod to connect one key stem 14 with the other. The connecting rod maintains the two key stems at the same height throughout the downward movement. The binding is thus prevented by preventing the tilting of the key stems 14, 14.
Another method of eliminating the binding problem is to use a dummy key connected to the same key cap to help guide the key stems.
The inclusion of the connecting rod increases the number of manufacturing steps as well as the number of constituent parts. These, in turn, lead to an increase in cost. The key board switch employing the dummy switch configuration also involves an inefficient utilization of the key board surface area, resulting, ultimately, in a higher cost.